1. Field of the Invention
The present invention relates to an audio outputting device such for example as a headphone device and a noise reducing audio outputting device. The present invention also relates to a noise reducing device used in these devices and a program for noise reduction processing.
2. Description of the Related Art
With the spread of portable type audio players, a noise reducing system that reduces noise of an external environment and thus provides a listener with a good reproduced sound field space in which the external noise is reduced has begun to be spread for use in headphones and earphones for the portable type audio players.
An example of this kind of noise reducing system is an active type noise reducing system that performs active noise reduction and which basically has the following constitution. External noise is collected by a microphone as acoustic-to-electric converting means. A noise reducing audio signal of acoustically opposite phase from the noise is generated from an audio signal of the collected noise. The generated noise reducing audio signal is acoustically reproduced by a speaker as electric-to-acoustic converting means, whereby the noise reducing audio signal and the noise are acoustically synthesized. Thus the noise is reduced (see Patent Document 1 (Japanese Patent No. 2778173)).
In this active type noise reducing system, in the past, a part for generating the noise reducing audio signal is formed by an analog circuit (analog filter), and is fixed as a filter circuit that can perform some degree of noise reduction in any noise environment.